Filesystem Hierarchy Standard

Edited by

RustyRussell

Edited by

DanielQuinlan

Edited by

ChristopherYeoh

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January 28 2004

Abstract

This standard consists of a set of requirements and guidelines for file
and directory placement under UNIX-like operating systems. The
guidelines are intended to support interoperability of applications,
system administration tools, development tools, and scripts as well as
greater uniformity of documentation for these systems.

Chapter 1. Introduction

1.1. Purpose

Software to predict the location of installed files and
directories, and

Users to predict the location of installed files and
directories.

We do this by:

Specifying guiding principles for each area of the filesystem,

Specifying the minimum files and directories required,

Enumerating exceptions to the principles, and

Enumerating specific cases where there has been historical conflict.

The FHS document is used by:

Independent software suppliers to create applications which are FHS
compliant, and work with distributions which are FHS compliant,

OS creators to provide systems which are FHS compliant, and

Users to understand and maintain the FHS compliance of a system.

The FHS document has a limited scope:

Local placement of local files is a local issue, so FHS does not
attempt to usurp system administrators.

FHS addresses issues where file placements need to be coordinated
between multiple parties such as local sites, distributions,
applications, documentation, etc.

1.2. Conventions

We recommend that you read a typeset version of this document rather
than the plain text version. In the typeset version, the names of files
and directories are displayed in a constant-width font.

Components of filenames that vary are represented by a description
of the contents enclosed in "<" and
">" characters, <thus>. Electronic mail addresses are also
enclosed in "<" and ">" but are shown in the usual
typeface.

Optional components of filenames are enclosed in
"[" and "]" characters and may
be combined with the "<" and
">" convention. For example, if a filename is
allowed to occur either with or without an extension, it might be
represented by
<filename>[.<extension>].

Variable substrings of directory names and filenames are indicated
by "*".

The sections of the text marked as
Rationale are explanatory and are
non-normative.

Chapter 2. The Filesystem

This standard assumes that the operating system underlying an
FHS-compliant file system supports the same basic security features
found in most UNIX filesystems.

It is possible to define two independent distinctions among
files: shareable vs. unshareable and variable vs. static. In general,
files that differ in either of these respects should be located in
different directories. This makes it easy to store files with
different usage characteristics on different filesystems.

"Shareable" files are those that can be stored on one host
and used on others. "Unshareable" files are those that are not
shareable. For example, the files in user home directories are
shareable whereas device lock files are not.

"Static" files include binaries, libraries, documentation
files and other files that do not change without system administrator
intervention. "Variable" files are files that are not static.

Rationale

Shareable files can be stored on one host and used on several
others. Typically, however, not all files in the filesystem
hierarchy are shareable and so each system has local storage
containing at least its unshareable files. It is convenient if all
the files a system requires that are stored on a foreign host can be
made available by mounting one or a few directories from the foreign
host.

Static and variable files should be segregated because static
files, unlike variable files, can be stored on read-only media and
do not need to be backed up on the same schedule as variable
files.

Historical UNIX-like filesystem hierarchies contained both
static and variable files under both /usr and
/etc. In order to realize the advantages
mentioned above, the /var hierarchy was
created and all variable files were transferred from
/usr to /var.
Consequently /usr can now be mounted read-only
(if it is a separate filesystem). Variable files have been
transferred from /etc to
/var over a longer period as technology has
permitted.

Here is an example of a FHS-compliant system.
(Other FHS-compliant layouts are possible.)

3.1. Purpose

The contents of the root filesystem must be adequate to boot,
restore, recover, and/or repair the system.

To boot a system, enough software and data must be present on the root partition
to mount other filesystems. This includes utilities, configuration,
boot loader information, and other essential start-up data.
/usr, /opt, and
/var are designed such that they may be located
on other partitions or filesystems.

To enable recovery and/or repair of a system, those utilities
needed by an experienced maintainer to diagnose and reconstruct a
damaged system must be present on the root filesystem.

To restore a system, those utilities needed to restore from
system backups (on floppy, tape, etc.) must be present on the root
filesystem.

Rationale

The minimum requirements for the root filesystem should be as
small as reasonably possible, but no smaller. While many users may
not want the extra complexity of a partitioned system, the option to
keep the root small should be preserved for several reasons:

It is occasionally mounted from very small media.

The root filesystem contains many system-specific configuration
files. Possible examples include a kernel that is specific to the
system, a specific hostname, etc. This means that the root filesystem
isn't always shareable between networked systems. Keeping it small on
servers in networked systems minimizes the amount of lost space for
areas of unshareable files. It also allows workstations with smaller
local hard drives.

While you may have the root filesystem on a large partition, and
may be able to fill it to your heart's content, there will be people
with smaller partitions. If you have more files installed, you may
find incompatibilities with other systems using root filesystems on
smaller partitions. If you are a developer then you may be turning
your assumption into a problem for a large number of users.

Disk errors that corrupt data on the root filesystem are a
greater problem than errors on any other partition. A small root
filesystem is less prone to corruption as the result of a system
crash.

These considerations must be balanced against the need for a
minimally useful operating environment, for the sake of the boot
process as well as in failure recovery situations.

Applications must never create or require special files or
subdirectories in the root directory. Other locations in the FHS
hierarchy provide more than enough flexibility for any package.

Rationale

There are several reasons why creating a new subdirectory of
the root filesystem is prohibited:

It demands space on a root partition which the system
administrator may want kept small and simple for either performance or
security reasons.

It evades whatever discipline the system administrator may have
set up for distributing standard file hierarchies across mountable
volumes.

Distributions should not create new directories in the root
hierarchy without extremely careful consideration of the consequences
including for application portability.

3.2. Requirements

The following directories, or symbolic links to directories, are
required in /.

Directory

Description

bin

Essential command binaries

boot

Static files of the boot loader

dev

Device files

etc

Host-specific system configuration

lib

Essential shared libraries and kernel modules

media

Mount point for removable media

mnt

Mount point for mounting a filesystem temporarily

opt

Add-on application software packages

run

Data relevant to running processes

sbin

Essential system binaries

srv

Data for services provided by this system

tmp

Temporary files

usr

Secondary hierarchy

var

Variable data

Each directory listed above is specified in detail in separate
subsections below. /usr and
/var each has a complete section in this
document due to the complexity of those directories.

3.3. Specific Options

The following directories, or symbolic links to directories,
must be in /, if the corresponding subsystem is
installed:

Directory

Description

home

User home directories (optional)

lib<qual>

Alternate format essential shared libraries (optional)

root

Home directory for the root user (optional)

Each directory listed above is specified in detail in separate
subsections below.

3.4. /bin : Essential user command binaries (for use by all users)

3.4.1. Purpose

/bin contains commands that may be used by
both the system administrator and by users, but which are required
when no other filesystems are mounted (e.g. in single user mode). It
may also contain commands which are used indirectly by scripts.
[1]

3.4.2. Requirements

There must be no subdirectories in /bin.

The following commands, or symbolic links to commands, are
required in /bin:

Command

Description

cat

Utility to concatenate files to standard output

chgrp

Utility to change file group ownership

chmod

Utility to change file access permissions

chown

Utility to change file owner and group

cp

Utility to copy files and directories

date

Utility to print or set the system data and time

dd

Utility to convert and copy a file

df

Utility to report filesystem disk space usage

dmesg

Utility to print or control the kernel message buffer

echo

Utility to display a line of text

false

Utility to do nothing, unsuccessfully

hostname

Utility to show or set the system's host name

kill

Utility to send signals to processes

ln

Utility to make links between files

login

Utility to begin a session on the system

ls

Utility to list directory contents

mkdir

Utility to make directories

mknod

Utility to make block or character special files

more

Utility to page through text

mount

Utility to mount a filesystem

mv

Utility to move/rename files

ps

Utility to report process status

pwd

Utility to print name of current working directory

rm

Utility to remove files or directories

rmdir

Utility to remove empty directories

sed

The `sed' stream editor

sh

POSIX compatible command shell

stty

Utility to change and print terminal line settings

su

Utility to change user ID

sync

Utility to flush filesystem buffers

true

Utility to do nothing, successfully

umount

Utility to unmount file systems

uname

Utility to print system information

If /bin/sh is not the POSIX compatible shell
command itself, it must be a hard or symbolic link to the real shell
command.

The [ and test
commands must be placed together in either /bin
or /usr/bin.

Rationale

Various shells behave differently when called as
sh, so as to preserve POSIX compatibility while
allowing changes or extensions to POSIX when desired.

The requirement for the [ and
test commands to be included as binaries (even if
implemented internally by the shell) is shared with the POSIX.2
standard.

3.4.3. Specific Options

The following programs, or symbolic links to programs, must be
in /bin if the corresponding subsystem is
installed:

Command

Description

csh

The C shell (optional)

ed

The `ed' editor (optional)

tar

The tar archiving utility (optional)

cpio

The cpio archiving utility (optional)

gzip

The GNU compression utility (optional)

gunzip

The GNU uncompression utility (optional)

zcat

The GNU uncompression utility (optional)

netstat

The network statistics utility (optional)

ping

The ICMP network test utility (optional)

/bin/csh may be a symbolic link to
/bin/tcsh or
/usr/bin/tcsh.

Rationale

The tar, gzip and cpio commands have been added to make restoration of a
system possible (provided that / is intact).

Conversely, if no restoration from the root partition is ever
expected, then these binaries might be omitted (e.g., a ROM chip root,
mounting /usr through NFS). If restoration of a
system is planned through the network, then ftp
or tftp (along with everything necessary to get
an ftp connection) must be available on the root partition.

3.5. /boot : Static files of the boot loader

3.5.1. Purpose

This directory contains everything required for the boot process
except configuration files not needed at boot time and the map
installer. Thus /boot stores data that is used before the kernel
begins executing user-mode programs. This may include saved master
boot sectors and sector map files.

Programs necessary to arrange for the boot loader to be able to
boot a file must be placed in /sbin.
Configuration files for boot loaders that are not required at boot
time must be placed in /etc.

3.5.2. Specific Options

3.6. /dev : Device files

3.6.1. Purpose

The /dev directory is the location of
special or device files.

3.6.2. Specific Options

If it is possible that devices in /dev will
need to be manually created, /dev must contain a
command named MAKEDEV, which can create devices
as needed. It may also contain a MAKEDEV.local
for any local devices.

If required, MAKEDEV must have provisions
for creating any device that may be found on the system, not just
those that a particular implementation installs.

3.7. /etc : Host-specific system configuration

3.7.1. Purpose

The /etc hierarchy contains configuration
files. A "configuration file" is a local file used to control the
operation of a program; it must be static and cannot be an executable
binary.
[3]

It is recommended that files be stored in subdirectories of
/etc rather than directly in
/etc.

3.7.2. Requirements

No binaries may be located under
/etc.

The following directories, or symbolic links to directories are
required in /etc:

Directory

Description

opt

Configuration for /opt

3.7.3. Specific Options

The following directories, or symbolic links to directories must
be in /etc, if the corresponding subsystem is
installed:

Directory

Description

X11

Configuration for the X Window system (optional)

sgml

Configuration for SGML (optional)

xml

Configuration for XML (optional)

The following files, or symbolic links to files, must be in
/etc if the corresponding subsystem is
installed:
[4]

File

Description

csh.login

Systemwide initialization file for C shell logins (optional)

exports

NFS filesystem access control list (optional)

fstab

Static information about filesystems (optional)

ftpusers

FTP daemon user access control list (optional)

gateways

File which lists gateways for routed (optional)

gettydefs

Speed and terminal settings used by getty (optional)

group

User group file (optional)

host.conf

Resolver configuration file (optional)

hosts

Static information about host names (optional)

hosts.allow

Host access file for TCP wrappers (optional)

hosts.deny

Host access file for TCP wrappers (optional)

hosts.equiv

List of trusted hosts for rlogin, rsh, rcp (optional)

hosts.lpd

List of trusted hosts for lpd (optional)

inetd.conf

Configuration file for inetd (optional)

inittab

Configuration file for init (optional)

issue

Pre-login message and identification file (optional)

ld.so.conf

List of extra directories to search for shared libraries (optional)

motd

Post-login message of the day file (optional)

mtab

Dynamic information about filesystems (optional)

mtools.conf

Configuration file for mtools (optional)

networks

Static information about network names (optional)

passwd

The password file (optional)

printcap

The lpd printer capability database (optional)

profile

Systemwide initialization file for sh shell logins (optional)

protocols

IP protocol listing (optional)

resolv.conf

Resolver configuration file (optional)

rpc

RPC protocol listing (optional)

securetty

TTY access control for root login (optional)

services

Port names for network services (optional)

shells

Pathnames of valid login shells (optional)

syslog.conf

Configuration file for syslogd (optional)

mtab does not fit the static nature of
/etc: it is excepted for historical reasons.
[5]

3.7.4. /etc/opt : Configuration files for /opt

3.7.4.1. Purpose

Host-specific configuration files for add-on application
software packages must be installed within the directory
/etc/opt/<subdir>, where
<subdir> is the name of the subtree in
/opt where the static data from that package is
stored.

3.7.4.2. Requirements

No structure is imposed on the internal arrangement of
/etc/opt/<subdir>.

If a configuration file must reside in a different location in
order for the package or system to function properly, it may be placed
in a location other than
/etc/opt/<subdir>.

Rationale

Refer to the rationale for /opt.

3.7.5. /etc/X11 : Configuration for the X Window System (optional)

3.7.5.1. Purpose

/etc/X11 is the location for all X11
host-specific configuration. This directory is necessary to allow
local control if /usr is mounted read
only.

3.7.5.2. Specific Options

The following files, or symbolic links to files, must be in
/etc/X11 if the corresponding subsystem is
installed:

File

Description

xorg.conf

The configuration file for X.org versions 7 and later (optional)

Xmodmap

Global X11 keyboard modification file (optional)

Subdirectories of /etc/X11 may include
those for xdm and for any other programs (some
window managers, for example) that need them.
[6]

3.7.6. /etc/sgml : Configuration files for SGML (optional)

3.7.6.1. Purpose

Generic configuration files defining high-level parameters of
the SGML systems are installed here. Files with names
*.conf indicate generic configuration files.
File with names *.cat are the DTD-specific
centralized catalogs, containing references to all other catalogs
needed to use the given DTD. The super catalog file
catalog references all the centralized
catalogs.

3.8. /home : User home directories (optional)

3.8.1. Purpose

/home is a fairly standard concept, but it
is clearly a site-specific filesystem.
[7]
The setup will differ from host to host. Therefore, no program should
rely on this location.
[8]

3.8.2. Requirements

User specific configuration files for applications are stored in the
user's home directory in a file that starts with the '.' character (a
"dot file"). If an application needs to create more than one dot file
then they should be placed in a subdirectory with a name starting with
a '.' character, (a "dot directory"). In this case the configuration
files should not start with the '.' character.
[9]

3.8.3. References

A number of efforts have been made to standardize the layout of home
directories, including the XDG Base Directories specification
[10]
and the GLib conventions on user directory contents.
[11]
To accomodate software which makes use of these conventions,
distributions may create directory hierarchies underneath home
directories which conform to them.

3.9. /lib : Essential shared libraries and kernel modules

3.9.1. Purpose

The /lib directory contains those shared
library images needed to boot the system and run the commands in the
root filesystem, ie. by binaries in /bin and
/sbin.
[12]

3.9.2. Requirements

At least one of each of the following filename patterns are
required (they may be files, or symbolic links):

File

Description

libc.so.*

The dynamically-linked C library (optional)

ld*

The execution time linker/loader (optional)

If a C preprocessor is installed, /lib/cpp
must be a reference to it, for historical reasons.
[13]

3.9.3. Specific Options

The following directories, or symbolic links to directories,
must be in /lib, if the corresponding subsystem
is installed:

3.10.1. Purpose

There may be one or more variants of the
/lib directory on systems which support more than
one binary format requiring separate libraries.
[14]

3.10.2. Requirements

If one or more of these directories exist, the requirements for
their contents are the same as the normal /lib
directory, except that /lib<qual>/cpp is
not required.
[15]

3.11. /media : Mount point for removable media

3.11.1. Purpose

This directory contains subdirectories which are used as mount
points for removable media such as floppy disks, cdroms and zip
disks.

Rationale

Historically there have been a number of other different places
used to mount removable media such as /cdrom,
/mnt or /mnt/cdrom. Placing
the mount points for all removable media directly in the root
directory would potentially result in a large number of extra
directories in /. Although the use of
subdirectories in /mnt as a mount point has
recently been common, it conflicts with a much older tradition of
using /mnt directly as a temporary mount point.

3.11.2. Specific Options

The following directories, or symbolic links to directories,
must be in /media, if the corresponding subsystem
is installed:

Directory

Description

floppy

Floppy drive (optional)

cdrom

CD-ROM drive (optional)

cdrecorder

CD writer (optional)

zip

Zip drive (optional)

On systems where more than one device exists for mounting a
certain type of media, mount directories can be created by appending a
digit to the name of those available above starting with '0', but the
unqualified name must also exist.
[16]

3.12. /mnt : Mount point for a temporarily mounted filesystem

3.12.1. Purpose

This directory is provided so that the system administrator may
temporarily mount a filesystem as needed. The content of this
directory is a local issue and should not affect the manner in which
any program is run.

This directory must not be used by installation programs: a
suitable temporary directory not in use by the system must be used
instead.

3.13. /opt : Add-on application software packages

3.13.1. Purpose

/opt is reserved for the installation of
add-on application software packages.

A package to be installed in /opt must
locate its static files in a separate
/opt/<package> or
/opt/<provider> directory
tree, where <package> is a name that
describes the software package and
<provider> is the provider's LANANA
registered name.

3.13.2. Requirements

Directory

Description

<package>

Static package objects

<provider>

LANANA registered provider name

The directories /opt/bin,
/opt/doc, /opt/include,
/opt/info, /opt/lib, and
/opt/man are reserved for local system
administrator use. Packages may provide "front-end" files intended to
be placed in (by linking or copying) these reserved directories by the
local system administrator, but must function normally in the absence
of these reserved directories.

Programs to be invoked by users must be located in the directory
/opt/<package>/bin or under the
/opt/<provider> hierarchy. If the package
includes UNIX manual pages, they must be located in
/opt/<package>/share/man or under the
/opt/<provider> hierarchy, and the same
substructure as /usr/share/man must be
used.

Package files that are variable (change in normal operation)
must be installed in /var/opt. See the section
on /var/opt for more information.

Host-specific configuration files must be installed in
/etc/opt. See the section on
/etc for more information.

No other package files may exist outside the
/opt, /var/opt, and
/etc/opt hierarchies except for those package
files that must reside in specific locations within the filesystem
tree in order to function properly. For example, device lock files
must be placed in /var/lock and devices must be
located in /dev.

Distributions may install software in /opt,
but must not modify or delete software installed by the local system
administrator without the assent of the local system
administrator.

Rationale

The use of /opt for add-on software is a
well-established practice in the UNIX community. The System V
Application Binary Interface [AT&T 1990], based on the System V
Interface Definition (Third Edition), provides for an
/opt structure very similar to the one defined
here.

The Intel Binary Compatibility Standard v. 2 (iBCS2) also
provides a similar structure for /opt.

Generally, all data required to support a package on a system
must be present within /opt/<package>,
including files intended to be copied into
/etc/opt/<package> and
/var/opt/<package> as well as reserved
directories in /opt.

The minor restrictions on distributions using
/opt are necessary because conflicts are possible
between distribution-installed and locally-installed software,
especially in the case of fixed pathnames found in some binary
software.

The structure of the directories below
/opt/<provider> is left up to the packager
of the software, though it is recommended that packages are installed
in /opt/<provider>/<package> and
follow a similar structure to the guidelines for
/opt/<package>. A valid reason for diverging from
this structure is for support packages which may have files installed
in /opt/<provider>/lib or
/opt/<provider>/bin.

3.14. /root : Home directory for the root user (optional)

3.14.1. Purpose

The root account's home directory may be determined by developer
or local preference, but this is the recommended default
location.
[17]

3.15. /run : Run-time variable data

3.15.1. Purpose

This directory contains system information data describing the
system since it was booted. Files under this directory must be
cleared (removed or truncated as appropriate) at the beginning of the
boot process.

The purposes of this directory were once served by
/var/run. In general, programs may continue to
use /var/run to fulfill the requirements set out
for /run for the purposes of backwards
compatibility. Programs which have migrated to use
/run should cease their usage of
/var/run, except as noted in the section on
/var/run.

Programs may have a subdirectory of
/run; this is encouraged for programs that
use more than one run-time file. Users may also have a subdirectory
of /run, although care must be taken to
appropriately limit access rights to prevent unauthorized use of
/run itself and other subdirectories.
[18]

3.15.2. Requirements

Process identifier (PID) files, which were originally placed in
/etc, must be placed in
/run. The naming convention for PID files is
<program-name>.pid. For example, the
crond PID file is named
/run/crond.pid.

The internal format of PID files remains unchanged. The file
must consist of the process identifier in ASCII-encoded decimal,
followed by a newline character. For example, if
crond was process number 25,
/run/crond.pid would contain three characters:
two, five, and newline.

Programs that read PID files should be somewhat flexible in what
they accept; i.e., they should ignore extra whitespace, leading
zeroes, absence of the trailing newline, or additional lines in the
PID file. Programs that create PID files should use the simple
specification located in the above paragraph.

System programs that maintain transient UNIX-domain sockets must
place them in this directory or an appropriate subdirectory as
outlined above.

3.16. /sbin : System binaries

3.16.1. Purpose

Utilities used for system administration (and other root-only
commands) are stored in /sbin,
/usr/sbin, and
/usr/local/sbin. /sbin
contains binaries essential for booting, restoring, recovering, and/or
repairing the system in addition to the binaries in
/bin.
[19]
Programs executed after
/usr is known to be mounted (when there are no
problems) are generally placed into /usr/sbin.
Locally-installed system administration programs should be placed into
/usr/local/sbin.
[20]

3.16.2. Requirements

There must be no subdirectories in /sbin.

The following commands, or symbolic links to commands, are
required in /sbin:

Command

Description

shutdown

Command to bring the system down.

3.16.3. Specific Options

The following files, or symbolic links to files, must be in
/sbin if the corresponding subsystem is
installed:

Command

Description

fastboot

Reboot the system without checking the disks (optional)

fasthalt

Stop the system without checking the disks (optional)

fdisk

Partition table manipulator (optional)

fsck

File system check and repair utility (optional)

fsck.*

File system check and repair utility for a specific filesystem (optional)

getty

The getty program (optional)

halt

Command to stop the system (optional)

ifconfig

Configure a network interface (optional)

init

Initial process (optional)

mkfs

Command to build a filesystem (optional)

mkfs.*

Command to build a specific filesystem (optional)

mkswap

Command to set up a swap area (optional)

reboot

Command to reboot the system (optional)

route

IP routing table utility (optional)

swapon

Enable paging and swapping (optional)

swapoff

Disable paging and swapping (optional)

update

Daemon to periodically flush filesystem buffers (optional)

3.17. /srv : Data for services provided by this system

3.17.1. Purpose

/srv contains site-specific data which is
served by this system.

Rationale

This main purpose of specifying this is so that users may find the
location of the data files for a particular service, and so that
services which require a single tree for readonly data, writable data
and scripts (such as cgi scripts) can be reasonably placed. Data that
is only of interest to a specific user should go in that users' home
directory. If the directory and file structure of the data is not
exposed to consumers, it should go in /var/lib.

The methodology used to name subdirectories of
/srv is unspecified as there is currently no
consensus on how this should be done. One method for structuring data
under /srv is by protocol,
eg. ftp, rsync,
www, and cvs. On large
systems it can be useful to structure /srv by
administrative context, such as /srv/physics/www,
/srv/compsci/cvs, etc. This setup will differ
from host to host. Therefore, no program should rely on a specific
subdirectory structure of /srv existing or data
necessarily being stored in /srv. However
/srv should always exist on FHS compliant systems
and should be used as the default location for such data.

Distributions must take care not to remove locally placed files in
these directories without administrator permission.
[21]

3.18. /tmp : Temporary files

3.18.1. Purpose

The /tmp directory must be made available
for programs that require temporary files.

Programs must not assume that any files or directories in
/tmp are preserved between invocations of the
program.

Rationale

IEEE standard P1003.2 (POSIX, part 2) makes requirements that
are similar to the above section.

Although data stored in /tmp may be deleted
in a site-specific manner, it is recommended that files and
directories located in /tmp be deleted whenever
the system is booted.

FHS added this recommendation on the basis of historical
precedent and common practice, but did not make it a requirement
because system administration is not within the scope of this
standard.

[1]
Command binaries that are not essential enough to place into
/bin must be placed in
/usr/bin, instead. Items that are required only
by non-root users (the X Window System, chsh,
etc.) are generally not essential enough to be placed into the root
partition.

[2] On some i386 machines, it may be necessary for
/boot to be located on a separate partition
located completely below cylinder 1024 of the boot device due to
hardware constraints.

Certain MIPS systems require a /boot
partition that is a mounted MS-DOS filesystem or whatever other
filesystem type is accessible for the firmware. This may result in
restrictions with respect to usable filenames within
/boot (only for affected systems).

[3]
To be clear, /etc may contain executable scripts,
such as the command scripts commonly called by
init to start and shut down the system and start
daemon processes. "Executable binary" in this context refers to
direct machine code or pseudocode not in a human-readable format, such
as native ELF executables.

[4]
Systems that use the shadow password suite will have additional
configuration files in /etc
(/etc/shadow and others) and programs in
/usr/sbin (useradd,
usermod, and others).

[5]
On some Linux systems, this may be a symbolic link to
/proc/mounts, in which case this exception is not
required.

[6] /etc/X11/xdm holds the configuration files for
xdm. These are most of the files previously
found in /usr/lib/X11/xdm. Some local variable
data for xdm is stored in
/var/lib/xdm.

[7]
Different people prefer to place user accounts in a variety of places.
This section describes only a suggested placement for user home
directories; nevertheless we recommend that all FHS-compliant
distributions use this as the default location for home
directories.

On small systems, each user's directory is typically one of the
many subdirectories of /home such as
/home/smith, /home/torvalds,
/home/operator, etc. On large systems
(especially when the /home directories are shared
amongst many hosts using NFS) it is useful to subdivide user home
directories. Subdivision may be accomplished by using subdirectories
such as /home/staff,
/home/guests,
/home/students, etc.

[8]
If you want to find out a user's home directory, you should use the
getpwent(3) library function rather than relying
on /etc/passwd because user information may be
stored remotely using systems such as NIS.

[9]
It is recommended that apart from autosave and lock files programs
should refrain from creating non dot files or directories in a home
directory without user intervention.

[12]
Shared libraries that are only necessary for binaries in
/usr (such as any X Window binaries) must not be
in /lib. Only the shared libraries required to
run binaries in /bin and
/sbin may be here. In particular, the library
libm.so.* may also be placed in
/usr/lib if it is not required by anything in
/bin or /sbin.

[14]
This is commonly used for 64-bit or 32-bit support on
systems which support multiple binary formats, but require libraries
of the same name. In this case, /lib32 and
/lib64 might be the library directories, and
/lib a symlink to one of them.

[15] /lib<qual>/cpp is still permitted: this
allows the case where /lib and
/lib<qual> are the same (one is a symbolic
link to the other).

[16]
A compliant implementation with two CDROM drives might have
/media/cdrom0 and
/media/cdrom1 with
/media/cdrom a symlink to either of these.

[17] If the home directory of the root account is not
stored on the root partition it will be necessary to make certain it
will default to / if it cannot be
located.

We recommend against using the root account for tasks that can be
performed as an unprivileged user, and that it be used solely for system
administration. For this reason, we recommend that subdirectories for
mail and other applications not appear in the root account's home
directory, and that mail for administration roles such as root,
postmaster, and webmaster be forwarded to an appropriate user.

[18] /run should not be writable for unprivileged
users; it is a major security problem if any user can write in this
directory. User-specific subdirectories should be writable only by
each directory's owner.

[20] Deciding what things go into
"sbin" directories is simple: if a normal (not a
system administrator) user will ever run it directly, then it must be
placed in one of the "bin" directories. Ordinary
users should not have to place any of the sbin
directories in their path.

For example, files such as chfn which users
only occasionally use must still be placed in
/usr/bin. ping, although it
is absolutely necessary for root (network recovery and diagnosis) is
often used by users and must live in /bin for
that reason.

We recommend that users have read and execute permission for
everything in /sbin except, perhaps, certain
setuid and setgid programs. The division between
/bin and /sbin was not
created for security reasons or to prevent users from seeing the
operating system, but to provide a good partition between binaries
that everyone uses and ones that are primarily used for administration
tasks. There is no inherent security advantage in making
/sbin off-limits for users.

[21]
This is particularly important as these areas will often contain both
files initially installed by the distributor, and those added by the
administrator.

4.1. Purpose

/usr is the second major section of the
filesystem. /usr is shareable, read-only data.
That means that /usr should be shareable between
various FHS-compliant hosts and must not be written to. Any
information that is host-specific or varies with time is stored
elsewhere.

Large software packages must not use a direct subdirectory under
the /usr hierarchy.

4.2. Requirements

The following directories, or symbolic links to directories, are
required in /usr.

Directory

Description

bin

Most user commands

include

Header files included by C programs

lib

Libraries

local

Local hierarchy (empty after main installation)

sbin

Non-vital system binaries

share

Architecture-independent data

4.3. Specific Options

Directory

Description

games

Games and educational binaries (optional)

libexec

Binaries run by other programs (optional)

lib<qual>

Alternate Format Libraries (optional)

src

Source code (optional)

An exception is made for the X Window System because of
considerable precedent and widely-accepted practice.

The following symbolic links to directories may be present. This
possibility is based on the need to preserve compatibility with older
systems until all implementations can be assumed to use the
/var hierarchy.

Once a system no longer requires any one of the above symbolic links,
the link may be removed, if desired.

4.4. /usr/bin : Most user commands

4.4.1. Purpose

This is the primary directory of executable commands on the
system.

4.4.2. Requirements

There must be no subdirectories in /usr/bin.

4.4.3. Specific Options

The following files, or symbolic links to files, must be in
/usr/bin, if the corresponding subsystem is
installed:

Command

Description

perl

The Practical Extraction and Report Language (optional)

python

The Python interpreted language (optional)

tclsh

Simple shell containing Tcl interpreter (optional)

wish

Simple Tcl/Tk windowing shell (optional)

expect

Program for interactive dialog (optional)

Rationale

Because shell script interpreters (invoked with
#!<path> on the first line of a shell
script) cannot rely on a path, it is advantageous to standardize their
locations. The POSIX shell and C-shell interpreters are already
fixed in /bin, but Perl, Python, and Tcl are
often found in many different places. They may be symlinks to the
physical location of the shell interpreters.

4.5. /usr/include : Directory for standard include files.

4.5.1. Purpose

This is where all of the system's general-use include files for the C
programming language should be placed.

4.5.2. Specific Options

The following directories, or symbolic links to directories,
must be in /usr/include, if the corresponding
subsystem is installed:

Directory

Description

bsd

BSD compatibility include files (optional)

4.6. /usr/lib : Libraries for programming and packages

4.6.1. Purpose

/usr/lib includes object files and libraries.
[22]
On some systems, it may also include internal binaries that are not
intended to be executed directly by users or shell scripts.
[23]

Applications may use a single subdirectory under
/usr/lib. If an application uses a subdirectory,
all architecture-dependent data exclusively used by the application
must be placed within that subdirectory.
[24]

4.6.2. Specific Options

For historical reasons, /usr/lib/sendmail
must be a symbolic link which resolves to the
sendmail-compatible command provided by the
system's mail transfer agent, if the latter exists.
[25][26]

4.7. /usr/libexec : Binaries run by other programs (optional)

4.7.1. Purpose

/usr/libexec includes internal binaries
that are not intended to be executed directly by users or shell
scripts. Applications may use a single subdirectory under
/usr/libexec.

Applications which use /usr/libexec in this
way must not also use /usr/lib to store internal
binaries, though they may use /usr/lib for the
other purposes documented here.

Rationale

Some previous versions of this document did not support
/usr/libexec, despite it being standard practice
in a number of environments.
[27]
To accomodate this restriction, it became common practice to use
/usr/lib instead. Either practice is now
acceptable, but each application must choose one way or the other to
organize itself.

4.8. /usr/lib<qual> : Alternate format libraries (optional)

4.8.1. Purpose

/usr/lib<qual> performs the same role as /usr/lib for an
alternate binary format, except that the symbolic links
/usr/lib<qual>/sendmail and /usr/lib<qual>/X11 are not required.
[28]

4.9. /usr/local : Local hierarchy

4.9.1. Purpose

The /usr/local hierarchy is for use by the
system administrator when installing software locally. It needs to be
safe from being overwritten when the system software is updated. It
may be used for programs and data that are shareable amongst a group
of hosts, but not found in /usr.

Locally installed software must be placed within
/usr/local rather than /usr
unless it is being installed to replace or upgrade software in
/usr.
[29]

4.9.2. Requirements

The following directories, or symbolic links to directories,
must be in /usr/local

Directory

Description

bin

Local binaries

etc

Host-specific system configuration for local binaries

games

Local game binaries

include

Local C header files

lib

Local libraries

man

Local online manuals

sbin

Local system binaries

share

Local architecture-independent hierarchy

src

Local source code

No other directories, except those listed below, may be in
/usr/local after first installing a FHS-compliant
system.

4.9.3. Specific Options

If directories /lib<qual> or
/usr/lib<qual> exist, the equivalent
directories must also exist in /usr/local.

/usr/local/etc may be a symbolic link to
/etc/local.

Rationale

The consistency of /usr/local/etc is
beneficial to installers, and is already used in other systems. As
all of /usr/local needs to be backed up to
reproduce a system, it introduces no additional maintenance overhead,
but a symlink to /etc/local is suitable if
systems want all their configuration under one hierarchy.

Note that /usr/etc is still not allowed: programs
in /usr should place configuration files in
/etc.

If the directory /usr/share/color exists as
specified in this document, then the directory
/usr/local/share/color must also exist, governed
by the same rules as /usr/share/color.

Rationale

This usage allows the sysadmin a place to install color profiles
manually when necessary.

4.9.4. /usr/local/share : Local architecture-independent hierarchy

The requirements for the contents of this directory are the same
as for /usr/share. The only additional constraint is
that /usr/local/share/man and
/usr/local/man directories must be synonomous
(usually this means that one of them must be a symbolic link).
[30]

4.10. /usr/sbin : Non-essential standard system binaries

4.10.1. Purpose

This directory contains any non-essential binaries used
exclusively by the system administrator. System administration
programs that are required for system repair, system recovery,
mounting /usr, or other essential functions must
be placed in /sbin instead.
[31]

4.10.2. Requirements

There must be no subdirectories in /usr/sbin.

4.11. /usr/share : Architecture-independent data

4.11.1. Purpose

The /usr/share hierarchy is for all
read-only architecture independent data files.
[32]

This hierarchy is intended to be shareable among all
architecture platforms of a given OS; thus, for example, a site with
i386, Alpha, and PPC platforms might maintain a single
/usr/share directory that is centrally-mounted.
Note, however, that /usr/share is generally not
intended to be shared by different OSes or by different releases of
the same OS.

Any program or package which contains or requires data that
doesn't need to be modified should store that data in
/usr/share (or
/usr/local/share, if installed locally). It is
recommended that a subdirectory be used in
/usr/share for this purpose. Applications using
a single file may use /usr/share/misc.

Game data stored in /usr/share/games must
be purely static data. Any modifiable files, such as score files,
game play logs, and so forth, should be placed in
/var/games.

4.11.2. Requirements

The following directories, or symbolic links to directories,
must be in /usr/share

Directory

Description

man

Online manuals

misc

Miscellaneous architecture-independent data

4.11.3. Specific Options

The following directories, or symbolic links to directories, must be in /usr/share, if the corresponding
subsystem is installed:

Directory

Description

color

Color management information (optional)

dict

Word lists (optional)

doc

Miscellaneous documentation (optional)

games

Static data files for /usr/games (optional)

info

Primary directory for GNU Info system (optional)

locale

Locale information (optional)

nls

Message catalogs for Native language support (optional)

ppd

Printer definitions (optional)

sgml

SGML data (optional)

terminfo

Directories for terminfo database (optional)

tmac

troff macros not distributed with groff (optional)

xml

XML data (optional)

zoneinfo

Timezone information and configuration (optional)

It is recommended that application-specific,
architecture-independent directories be placed here. Such directories
include groff, perl,
ghostscript, texmf, and
kbd (Linux) or syscons
(BSD). They may, however, be placed in /usr/lib
for backwards compatibility, at the distributor's discretion.
Similarly, a /usr/lib/games hierarchy may be used
in addition to the /usr/share/games hierarchy if
the distributor wishes to place some game data there.

4.11.4. /usr/share/color : Color management information (optional)

4.11.4.1. Purpose

This directory is the home for ICC color management files
installed by the system.

4.11.4.2. Specific
Options

The following directories must be in
/usr/share/color, if the corresponding subsystem
is installed:

Directory

Description

icc

ICC color profiles (optional)

The top-level directory /usr/share/color
must not contain any files; all files should be in subdirectories of
/usr/share/color.

4.11.5. /usr/share/dict : Word lists (optional)

4.11.5.1. Purpose

This directory is the home for word lists on the system;
Traditionally this directory contains only the English
words file, which is used by
look(1) and various spelling programs.
words may use either American or British
spelling.

Rationale

The reason that only word lists are located here is that they
are the only files common to all spell checkers.

4.11.5.2. Specific Options

The following files, or symbolic links to files, must be in
/usr/share/dict, if the corresponding subsystem
is installed:

File

Description

words

List of English words (optional)

Sites that require both American and British spelling may link
words to
­/usr/share/dict/american-english or
­/usr/share/dict/british-english.

Word lists for other languages may be added using the English
name for that language, e.g.,
/usr/share/dict/french,
/usr/share/dict/danish, etc. These should, if
possible, use a character set based on Unicode, with the UTF-8
character set being the preferred option.

Other word lists must be included here, if present.

4.11.6. /usr/share/man : Manual pages

4.11.6.1. Purpose

This section details the organization for manual pages
throughout the system, including /usr/share/man.
Also refer to the section on
/var/cache/man.

The primary <mandir> of the system is
/usr/share/man.
/usr/share/man contains manual information for
commands and data under the / and
/usr filesystems.
[33]

Manual pages are stored in
<mandir>/<locale>/man<section>/<arch>.
An explanation of <mandir>,
<locale>,
<section>, and
<arch> is given below.

A description of each section follows:

man1: User programs
Manual pages that describe publicly accessible commands are contained in
this chapter. Most program documentation that a user will need to use
is located here.

man2: System calls
This section describes all of the system calls (requests for the
kernel to perform operations).

man3: Library functions and subroutines
Section 3 describes program library routines that are not direct calls
to kernel services. This and chapter 2 are only really of interest to
programmers.

man4: Special files
Section 4 describes the special files, related driver functions, and
networking support available in the system. Typically, this includes
the device files found in /dev and the kernel interface to
networking protocol support.

man5: File formats
The formats for many data files are documented in the
section 5. This includes various include files, program output files,
and system files.

man6: Games
This chapter documents games, demos, and generally trivial programs.
Different people have various notions about how essential this is.

man7: Miscellaneous
Manual pages that are difficult to classify are designated as being
section 7. The troff and other text processing macro packages are found
here.

man8: System administration
Programs used by system administrators for system operation and
maintenance are documented here. Some of these programs are also
occasionally useful for normal users.

4.11.6.2. Specific Options

The following directories, or symbolic links to directories,
must be in
/usr/share/<mandir>/<locale>, unless
they are empty:
[34]

Directory

Description

man1

User programs (optional)

man2

System calls (optional)

man3

Library calls (optional)

man4

Special files (optional)

man5

File formats (optional)

man6

Games (optional)

man7

Miscellaneous (optional)

man8

System administration (optional)

The component <section> describes the
manual section.

Provisions must be made in the structure of
/usr/share/man to support manual pages which are
written in different (or multiple) languages. These provisions must
take into account the storage and reference of these manual pages.
Relevant factors include language (including geographical-based
differences), and character code set.

This naming of language subdirectories of
/usr/share/man is based on Appendix E of the
POSIX 1003.1 standard which describes the locale identification string
— the most well-accepted method to describe a cultural
environment. The <locale> string
is:

<language>[_<territory>][.<character-set>][,<version>]

The <language> field must be taken
from ISO 639 (a code for the representation of names of languages).
It must be two characters wide and specified with lowercase letters
only.

The <territory> field must be the
two-letter code of ISO 3166 (a specification of representations of
countries), if possible. (Most people are familiar with the
two-letter codes used for the country codes in email addresses.) It
must be two characters wide and specified with uppercase letters
only.
[35]

The <character-set> field must
represent the standard describing the character set. If the
­<character-set> field is just a
numeric specification, the number represents the number of the
international standard describing the character set. It is
recommended that this be a numeric representation if possible (ISO
standards, especially), not include additional punctuation symbols,
and that any letters be in lowercase.

A parameter specifying a <version> of
the profile may be placed after the
­<character-set> field, delimited by a
comma. This may be used to discriminate between different cultural
needs; for instance, dictionary order versus a more systems-oriented
collating order. This standard recommends not using the
<version> field, unless it is
necessary.

Systems which use a unique language and code set for all manual
pages may omit the <locale> substring and
store all manual pages in <mandir>. For
example, systems which only have English manual pages coded with
ASCII, may store manual pages (the
man<section> directories) directly in
/usr/share/man. (That is the traditional
circumstance and arrangement, in fact.)

Countries for which there is a well-accepted standard character
code set may omit the ­<character-set>
field, but it is strongly recommended that it be included, especially
for countries with several competing standards.

Various examples:

Language

Territory

Character Set

Directory

English

—

ASCII

/usr/share/man/en

English

United Kingdom

Unicode UTF-8

/usr/share/man/en_GB.10646

English

United States

ASCII

/usr/share/man/en_US

French

Canada

ISO 8859-1

/usr/share/man/fr_CA.88591

French

France

ISO 8859-1

/usr/share/man/fr_FR.88591

German

Germany

ISO 646

/usr/share/man/de_DE.646

German

Germany

ISO 6937

/usr/share/man/de_DE.6937

German

Germany

ISO 8859-1

/usr/share/man/de_DE.88591

German

Switzerland

ISO 646

/usr/share/man/de_CH.646

Japanese

Japan

JIS

/usr/share/man/ja_JP.jis

Japanese

Japan

SJIS

/usr/share/man/ja_JP.sjis

Japanese

Japan

UJIS (or EUC-J)

/usr/share/man/ja_JP.ujis

Japanese

Japan

Unicode UTF-16

/usr/share/man/ja_JP.10646

Similarly, provision must be made for manual pages which are
architecture-dependent, such as documentation on device-drivers or
low-level system administration commands. These must be placed under
an <arch> directory in the appropriate
man<section> directory; for example, a man
page for the i386 ctrlaltdel(8) command might be placed in
/usr/share/man/<locale>/man8/i386/ctrlaltdel.8.

Manual pages for commands and data under
/usr/local are stored in
/usr/local/man. It follows that all
manual page hierarchies in the system must have the same structure as
/usr/share/man.

The cat page sections (cat<section>)
containing formatted manual page entries are also found within
subdirectories of <mandir>/<locale>,
but are not required nor may they be distributed in lieu of nroff
source manual pages.

The numbered sections "1" through "8" are traditionally defined.
In general, the file name for manual pages located within a particular
section end with .<section>.

In addition, some large sets of application-specific manual
pages have an additional suffix appended to the manual page filename.
For example, the MH mail handling system manual pages must have
mh appended to all MH manuals. All X Window
System manual pages must have an x appended to
the filename.

The practice of placing various language manual pages in
appropriate subdirectories of /usr/share/man also
applies to the other manual page hierarchies, such as
/usr/local/man. (This portion of the standard
also applies later in the section on the optional
/var/cache/man structure.)

4.11.7. /usr/share/misc : Miscellaneous architecture-independent data

4.11.7.1. Specific Options

The following files, or symbolic links to files, must be in
/usr/share/misc, if the corresponding subsystem
is installed:

File

Description

ascii

ASCII character set table (optional)

termcap

Terminal capability database (optional)

termcap.db

Terminal capability database (optional)

Other (application-specific) files may appear here, but a distributor
may place them in /usr/lib at their discretion.
[36][37]

4.11.8. /usr/share/ppd : Printer definitions (optional)

4.11.8.1. Purpose

/usr/share/ppd contains PostScript Printer
Definition (PPD) files, which are used as descriptions of printer
drivers by many print systems. PPD files may be placed in this
directory, or in a subdirectory.

4.11.9. /usr/share/sgml : SGML data (optional)

4.11.9.1. Purpose

/usr/share/sgml contains
architecture-independent files used by SGML applications, such
as ordinary catalogs (not the centralized ones, see
/etc/sgml), DTDs, entities, or style
sheets.

4.11.9.2. Specific Options

The following directories, or symbolic links to directories,
must be in /usr/share/sgml, if the corresponding
subsystem is installed:

Directory

Description

docbook

docbook DTD (optional)

tei

tei DTD (optional)

html

html DTD (optional)

mathml

mathml DTD (optional)

Other files that are not specific to a given DTD may reside in
their own subdirectory.

4.11.10. /usr/share/xml : XML data (optional)

4.11.10.1. Purpose

/usr/share/xml contains
architecture-independent files used by XML applications, such
as ordinary catalogs (not the centralized ones, see
/etc/sgml), DTDs, entities, or style
sheets.

4.11.10.2. Specific Options

The following directories, or symbolic links to directories,
must be in /usr/share/xml, if the corresponding
subsystem is installed:

Directory

Description

docbook

docbook XML DTD (optional)

xhtml

XHTML DTD (optional)

mathml

MathML DTD (optional)

4.12. /usr/src : Source code (optional)

4.12.1. Purpose

Source code may be placed in this
subdirectory, only for reference purposes.
[38]

[22] Miscellaneous
architecture-independent application-specific static files and
subdirectories must be placed in /usr/share.

[23] See below, in the /usr/libexec
section, for a discussion of /usr/lib
vs. /usr/libexec for executable binaries.

[24] For example, the perl5 subdirectory for
Perl 5 modules and libraries.

[25]
Some executable commands such as makewhatis and
sendmail have also been traditionally placed in
/usr/lib. makewhatis is an
internal binary and must be placed in a binary directory; users access
only catman. Newer sendmail
binaries are now placed by default in /usr/sbin.
Additionally, systems using a sendmail-compatible
mail transfer agent must provide /usr/sbin/sendmail
as the sendmail command, either as the executable
itself or as a symlink to the appropriate executable.

[26]
Host-specific data for the X Window System must not be stored in
/usr/lib/X11. Host-specific configuration files
such as xorg.conf must be stored in
/etc/X11. This includes configuration data such
as system.twmrc even if it is only made a
symbolic link to a more global configuration file (probably in
/usr/lib/X11).

[27] See, for example, the "GNU Coding Standards" from
the Free Software Foundation.

[28]
The case where /usr/lib and /usr/lib<qual> are the
same (one is a symbolic link to the other) these files and the
per-application subdirectories will exist.

[29]
Software placed in / or
/usr may be overwritten by system upgrades
(though we recommend that distributions do not overwrite data in
/etc under these circumstances). For this
reason, local software must not be placed outside of
/usr/local without good reason.

[30] /usr/local/man may be deprecated in future FHS
releases, so if all else is equal, making that one a symlink seems
sensible.

[31]
Locally installed system administration programs should be placed in
/usr/local/sbin.

[32]
Much of this data originally lived in /usr
(man, doc) or
/usr/lib (dict,
terminfo, zoneinfo).

[33] Obviously, there are no manual pages in /
because they are not required at boot time nor are they required in
emergencies. Really.

[34] For example, if /usr/local/man
has no manual pages in section 4 (Devices), then
/usr/local/man/man4 may be omitted.

[35] A major exception to this rule is the
United Kingdom, which is `GB' in the ISO 3166, but `UK' for most email
addresses.

[37]
Historically, the magic file was placed in
/usr/share/misc, but modern variants of the file
command use several files and place them in
/usr/share/file. For compatibility,
implementations may create a symlink at
/usr/share/misc/magic, pointing to
/usr/share/file/magic.

5.1. Purpose

/var contains variable data files. This
includes spool directories and files, administrative and logging data,
and transient and temporary files.

Some portions of /var are not shareable
between different systems. For instance,
/var/log, /var/lock, and
/var/run. Other portions may be shared, notably
/var/mail, /var/cache/man,
/var/cache/fonts, and
/var/spool/news.

/var is specified here in order to make it
possible to mount /usr read-only. Everything
that once went into /usr that is written to
during system operation (as opposed to installation and software
maintenance) must be in /var.

If /var cannot be made a separate
partition, it is often preferable to move /var
out of the root partition and into the /usr
partition. (This is sometimes done to reduce the size of the root
partition or when space runs low in the root partition.) However,
/var must not be linked to
/usr because this makes separation of
/usr and /var more difficult
and is likely to create a naming conflict. Instead, link
/var to /usr/var.

Applications must generally not add directories to the top level
of /var. Such directories should only be added
if they have some system-wide implication, and in consultation with
the FHS mailing list.

5.2. Requirements

The following directories, or symbolic links to directories, are
required in /var:

Directory

Description

cache

Application cache data

lib

Variable state information

local

Variable data for /usr/local

lock

Lock files

log

Log files and directories

opt

Variable data for /opt

run

Data relevant to running processes

spool

Application spool data

tmp

Temporary files preserved between system reboots

Several directories are `reserved' in the sense that they must
not be used arbitrarily by some new application, since they would
conflict with historical and/or local practice. They are:

/var/backups
/var/cron
/var/msgs
/var/preserve

5.3. Specific Options

The following directories, or symbolic links to directories,
must be in /var, if the corresponding subsystem
is installed:

Directory

Description

account

Process accounting logs (optional)

crash

System crash dumps (optional)

games

Variable game data (optional)

mail

User mailbox files (optional)

yp

Network Information Service (NIS) database files (optional)

5.4. /var/account : Process accounting logs (optional)

5.4.1. Purpose

This directory holds the current active process accounting log
and the composite process usage data (as used in some UNIX-like
systems by lastcomm and
sa).

5.5. /var/cache : Application cache data

5.5.1. Purpose

/var/cache is intended for cached data from
applications. Such data is locally generated as a result of
time-consuming I/O or calculation. The application must be able to
regenerate or restore the data. Unlike
/var/spool, the cached files can be deleted
without data loss. The data must remain valid between invocations of
the application and rebooting the system.

Files located under /var/cache may be
expired in an application specific manner, by the system
administrator, or both. The application must always be able to
recover from manual deletion of these files (generally because of a
disk space shortage). No other requirements are made on the data
format of the cache directories.

Rationale

The existence of a separate directory for cached data allows
system administrators to set different disk and backup policies from
other directories in /var.

5.5.2. Specific Options

Directory

Description

fonts

Locally-generated fonts (optional)

man

Locally-formatted manual pages (optional)

www

WWW proxy or cache data (optional)

<package>

Package specific cache data (optional)

5.5.3. /var/cache/fonts : Locally-generated fonts (optional)

5.5.3.1. Purpose

The directory /var/cache/fonts should be used to store any
dynamically-created fonts. In particular, all of the fonts which are
automatically generated by mktexpk must be located in
appropriately-named subdirectories of /var/cache/fonts.
[39]

5.5.3.2. Specific Options

Other dynamically created fonts may also be placed in this tree,
under appropriately-named subdirectories of
/var/cache/fonts.

5.5.4. /var/cache/man : Locally-formatted manual pages (optional)

5.5.4.1. Purpose

This directory provides a standard location for sites that provide a
read-only /usr partition, but wish to allow caching of
locally-formatted man pages. Sites that mount /usr as writable
(e.g., single-user installations) may choose not to use
/var/cache/man and may write formatted man pages into the
cat<section> directories in /usr/share/man directly. We
recommend that most sites use one of the following options instead:

Preformat all manual pages alongside the unformatted versions.

Allow no caching of formatted man pages, and require formatting to be
done each time a man page is brought up.

Allow local caching of formatted man pages in /var/cache/man.

The structure of /var/cache/man needs to
reflect both the fact of multiple man page hierarchies and the
possibility of multiple language support.

Given an unformatted manual page that normally appears in
<path>/man/<locale>/man<section>,
the directory to place formatted man pages in is
/var/cache/man/<catpath>/<locale>/cat<section>,
where <catpath> is derived from
<path> by removing any leading
usr and/or trailing share
pathname components. (Note that the
<locale> component may be missing.)
[40]

Man pages written to /var/cache/man may
eventually be transferred to the appropriate preformatted directories
in the source man hierarchy or expired; likewise
formatted man pages in the source man hierarchy
may be expired if they are not accessed for a period of time.

If preformatted manual pages come with a system on read-only
media (a CD-ROM, for instance), they must be installed in the source
man hierarchy
(e.g. /usr/share/man/cat<section>).
/var/cache/man is reserved as a writable cache
for formatted manual pages.

Rationale

Release 1.2 of the standard specified
/var/catman for this hierarchy. The path has
been moved under /var/cache to better reflect the
dynamic nature of the formatted man pages. The directory name has
been changed to man to allow for enhancing the
hierarchy to include post-processed formats other than "cat", such as
PostScript, HTML, or DVI.

5.6. /var/crash : System crash dumps (optional)

5.6.1. Purpose

This directory holds system crash dumps. As of the date of this
release of the standard, system crash dumps were not supported under
Linux but may be supported by other systems which may comply with the
FHS.

5.7. /var/games : Variable game data (optional)

5.7.1. Purpose

Any variable data relating to games in /usr
should be placed here. /var/games should hold
the variable data previously found in /usr;
static data, such as help text, level descriptions, and so on, must
remain elsewhere, such as
/usr/share/games.

Rationale

/var/games has been given a hierarchy of
its own, rather than leaving it merged in with the old
/var/lib as in release 1.2. The separation
allows local control of backup strategies, permissions, and disk
usage, as well as allowing inter-host sharing and reducing clutter in
/var/lib. Additionally,
/var/games is the path traditionally used by BSD.

5.8. /var/lib : Variable state information

5.8.1. Purpose

This hierarchy holds state information pertaining to an
application or the system. State information is data that programs
modify while they run, and that pertains to one specific host. Users
must never need to modify files in /var/lib to
configure a package's operation, and the specific file hierarchy
used to store the data must not be exposed to regular users.
[41]

State information is generally used to preserve the condition of
an application (or a group of inter-related applications) between
invocations and between different instances of the same application.
State information should generally remain valid after a reboot, should
not be logging output, and should not be spooled data.

An application (or a group of inter-related applications) must
use a subdirectory of /var/lib for its data.
There is one required subdirectory,
/var/lib/misc, which is intended for state files
that don't need a subdirectory; the other subdirectories should only
be present if the application in question is included in the
distribution.
[42]

/var/lib/<name> is the location that
must be used for all distribution packaging support. Different
distributions may use different names, of course.

5.8.2. Requirements

The following directories, or symbolic links to directories, are
required in /var/lib:

Directory

Description

misc

Miscellaneous state data

5.8.3. Specific Options

The following directories, or symbolic links to directories, must be in /var/lib, if the
corresponding subsystem is installed:

Directory

Description

<editor>

Editor backup files and state (optional)

<pkgtool>

Packaging support files (optional)

<package>

State data for packages and subsystems (optional)

color

Color management information (optional)

hwclock

State directory for hwclock (optional)

xdm

X display manager variable data (optional)

5.8.4. /var/lib/<editor> : Editor backup files and state (optional)

5.8.4.1. Purpose

Other editors may not require a directory for crash-recovery
files, but may require a well-defined place to store other information
while the editor is running. This information should be stored in a
subdirectory under /var/lib (for example, GNU
Emacs would place lock files in
/var/lib/emacs/lock).

Future editors may require additional state information beyond
crash-recovery files and lock files — this information should
also be placed under
/var/lib/<editor>.

Rationale

Previous Linux releases, as well as all commercial vendors, use
/var/preserve for vi or its clones. However,
each editor uses its own format for these crash-recovery files, so a
separate directory is needed for each editor.

Editor-specific lock files are usually quite different from the
device or resource lock files that are stored in
/var/lock and, hence, are stored under
/var/lib.

5.8.5. /var/lib/color : Color management information (optional)

5.8.5.1. Purpose

This directory is the home for ICC color management files
installed dynamically. This directory shall be laid out using the
same rules as the /usr/share/color
directory.

5.8.6. /var/lib/hwclock : State directory for hwclock (optional)

5.8.6.1. Purpose

This directory contains the file
/var/lib/hwclock/adjtime.

Rationale

In FHS 2.1, this file was /etc/adjtime, but
as hwclock updates it, that was obviously
incorrect.

5.8.7. /var/lib/misc : Miscellaneous variable data

5.8.7.1. Purpose

This directory contains variable data not placed in a
subdirectory in /var/lib. An attempt should be
made to use relatively unique names in this directory to avoid
namespace conflicts.
[43]

5.9. /var/lock : Lock files

5.9.1. Purpose

Lock files should be stored within the
/var/lock directory structure.

Lock files for devices and other resources shared by multiple
applications, such as the serial device lock files that were
originally found in either /usr/spool/locks or
/usr/spool/uucp, must now be stored in
/var/lock. The naming convention which must be
used is "LCK.." followed by the base name of the device. For example,
to lock /dev/ttyS0 the file "LCK..ttyS0" would be created.
[44]

The format used for the contents of such lock files must be the
HDB UUCP lock file format. The HDB format is to store the process
identifier (PID) as a ten byte ASCII decimal number, with a trailing
newline. For example, if process 1230 holds a lock file, it would
contain the eleven characters: space, space, space, space, space,
space, one, two, three, zero, and newline.

5.10. /var/log : Log files and directories

5.10.1. Purpose

This directory contains miscellaneous log files. Most logs must
be written to this directory or an appropriate subdirectory.

5.10.2. Specific Options

The following files, or symbolic links to files, must be in
/var/log, if the corresponding subsystem is
installed:

File

Description

lastlog

record of last login of each user

messages

system messages from syslogd

wtmp

record of all logins and logouts

5.11. /var/mail : User mailbox files (optional)

5.11.1. Purpose

The mail spool must be accessible through
/var/mail and the mail spool files must take the
form <username>.
[45]

User mailbox files in this location must be stored in the standard
UNIX mailbox format.

Rationale

The logical location for this directory was changed from
/var/spool/mail in order to bring FHS in-line
with nearly every UNIX implementation. This change is important for
inter-operability since a single /var/mail is
often shared between multiple hosts and multiple UNIX implementations
(despite NFS locking issues).

It is important to note that there is no requirement to
physically move the mail spool to this location. However, programs
and header files must be changed to use
/var/mail.

5.12. /var/opt : Variable data for /opt

5.12.1. Purpose

Variable data of the packages in /opt must
be installed in /var/opt/<subdir>, where
<subdir> is the name of the subtree in
/opt where the static data from an add-on
software package is stored, except where superseded by another file in
/etc. No structure is imposed on the internal
arrangement of /var/opt/<subdir>.

Rationale

Refer to the rationale for /opt.

5.13. /var/run : Run-time variable data

5.13.1. Purpose

This directory was once intended for system information data
describing the system since it was booted. These functions have been
moved to /run; this directory exists to ensure
compatibility with systems and software using an older version of this
specification.

5.13.2. Requirements

In general, the requirements for /run shall
also apply to /var/run. It is valid to implement
/var/run as a symlink to
/run.

The utmp file, which stores information
about who is currently using the system, is located in this
directory.

Programs should not access both /var/run
and /run directly, except to access
/var/run/utmp.
[46]

5.14. /var/spool : Application spool data

5.14.1. Purpose

/var/spool contains data which is awaiting
some kind of later processing. Data in
/var/spool represents work to be done in the
future (by a program, user, or administrator); often data is deleted
after it has been processed.
[47]

5.14.2. Specific Options

The following directories, or symbolic links to directories,
must be in /var/spool, if the corresponding
subsystem is installed:

Directory

Description

lpd

Printer spool directory (optional)

mqueue

Outgoing mail queue (optional)

news

News spool directory (optional)

rwho

Rwhod files (optional)

uucp

Spool directory for UUCP (optional)

5.14.3. /var/spool/lpd : Line-printer daemon print queues (optional)

5.14.3.1. Purpose

The lock file for lpd,
lpd.lock, must be placed in
/var/spool/lpd. It is suggested that the lock
file for each printer be placed in the spool directory for that
specific printer and named lock.

5.14.3.2. Specific Options

Directory

Description

printer

Spools for a specific printer (optional)

5.14.4. /var/spool/rwho : Rwhod files (optional)

5.14.4.1. Purpose

This directory holds the rwhod information
for other systems on the local net.

Rationale

Some BSD releases use /var/rwho for this
data; given its historical location in /var/spool
on other systems and its approximate fit to the definition of
`spooled' data, this location was deemed more appropriate.

5.15. /var/tmp : Temporary files preserved between system reboots

5.15.1. Purpose

The /var/tmp directory is made available
for programs that require temporary files or directories that are
preserved between system reboots. Therefore, data stored in
/var/tmp is more persistent than data in
/tmp.

Files and directories located in /var/tmp
must not be deleted when the system is booted. Although data stored
in /var/tmp is typically deleted in a
site-specific manner, it is recommended that deletions occur at a less
frequent interval than /tmp.

5.16.1. Purpose

Variable data for the Network Information Service (NIS),
formerly known as the Sun Yellow Pages (YP), must be placed in this
directory.

Rationale

/var/yp is the standard directory for NIS
(YP) data and is almost exclusively used in NIS documentation and
systems.
[48]

[39]
This standard does not currently incorporate the TeX Directory
Structure (a document that describes the layout TeX files and
directories), but it may be useful reading. It is located at
ftp://ctan.tug.org/tex/

[40]
For example, /usr/share/man/man1/ls.1 is
formatted into /var/cache/man/cat1/ls.1, and
/usr/X11R6/man/<locale>/man3/XtClass.3x into
/var/cache/man/X11R6/<locale>/cat3/XtClass.3x.

This section is for additional requirements and recommendations
that only apply to a specific operating system. The material in this
section should never conflict with the base standard.

6.1. Linux

This is the annex for the Linux operating system.

6.1.1. / : Root directory

On Linux systems, if the kernel is located in
/, we recommend using the names
vmlinux or vmlinuz, which
have been used in recent Linux kernel source packages.

6.1.2. /bin : Essential user command binaries (for use by all users)

Linux systems which require them place these additional files into
/bin:

setserial

6.1.3. /dev : Devices and special files

The following devices must exist under /dev.

/dev/null

All data written to this device is discarded. A read from this device
will return an EOF condition.

/dev/zero

This device is a source of zeroed out data. All data written to this
device is discarded. A read from this device will return as many bytes
containing the value zero as was requested.

/dev/tty

This device is a synonym for the controlling terminal of a
process. Once this device is opened, all reads and writes will behave
as if the actual controlling terminal device had been opened.

Rationale

Previous versions of the FHS had stricter requirements for
/dev. Other devices may also exist in
/dev. Device names may exist as symbolic links to other device nodes
located in /dev or subdirectories of /dev. There is no requirement
concerning major/minor number values.

6.1.4. /etc : Host-specific system configuration

Linux systems which require them place these additional files into
/etc.

lilo.conf

6.1.5. /proc : Kernel and process information virtual filesystem

The proc filesystem is the de-facto
standard Linux method for handling process and system information,
rather than /dev/kmem and other similar methods.
We strongly encourage this for the storage and retrieval of process
information as well as other kernel and memory information.

6.1.6. /sbin : Essential system binaries

Static ln (sln) and
static sync (ssync) are
useful when things go wrong. The primary use of
sln (to repair incorrect symlinks in
/lib after a poorly orchestrated upgrade) is no
longer a major concern now that the ldconfig
program (usually located in /usr/sbin) exists and
can act as a guiding hand in upgrading the dynamic libraries. Static
sync is useful in some emergency situations.
Note that these need not be statically linked versions of the standard
ln and sync, but may
be.

The ldconfig binary is optional for
/sbin since a site may choose to run
ldconfig at boot time, rather than only when
upgrading the shared libraries. (It's not clear whether or not it is
advantageous to run ldconfig on each boot.) Even
so, some people like ldconfig around for the
following (all too common) situation:

I've just removed /lib/<file>.

I can't find out the name of the library because ls is
dynamically linked, I'm using a shell that doesn't have ls
built-in, and I don't know about using "echo *" as a
replacement.

I have a static sln, but I don't know what to call the link.

Miscellaneous:

ctrlaltdel

kbdrate

So as to cope with the fact that some keyboards come up with
such a high repeat rate as to be unusable,
kbdrate may be installed in
/sbin on some systems.

Since the default action in the kernel for the Ctrl-Alt-Del key
combination is an instant hard reboot, it is generally advisable to
disable the behavior before mounting the root filesystem in read-write
mode. Some init suites are able to disable
Ctrl-Alt-Del, but others may require the
ctrlaltdel program, which may be installed in
/sbin on those systems.

6.1.7. /sys : Kernel and system information virtual filesystem

The sys filesystem is the location where
information about devices, drivers, and some kernel features is
exposed. Its underlying structure is determined by the particular
Linux kernel being used at the moment, and is otherwise
unspecified.

6.1.8. /usr/include : Header files included by C programs

These symbolic links are required if a C or C++ compiler is
installed and only for systems not based on glibc.

7.2. Background of the FHS

The process of developing a standard filesystem hierarchy began
in August 1993 with an effort to restructure the file and directory
structure of Linux. The FSSTND, a filesystem hierarchy standard
specific to the Linux operating system, was released on February 14,
1994. Subsequent revisions were released on October 9, 1994 and March
28, 1995.

In early 1995, the goal of developing a more comprehensive
version of FSSTND to address not only Linux, but other UNIX-like
systems was adopted with the help of members of the BSD development
community. As a result, a concerted effort was made to focus on
issues that were general to UNIX-like systems. In recognition of this
widening of scope, the name of the standard was changed to Filesystem
Hierarchy Standard or FHS for short.

Volunteers who have contributed extensively to this standard are
listed at the end of this document. This standard represents a
consensus view of those and other contributors.

Thanks to Network Operations at the University of California at
San Diego, and later to SourceForge, who allowed us to use their
excellent mailing list servers during earlier phases of development.

7.3. General Guidelines

Here are some of the guidelines that have been used in the development
of this standard:

Solve technical problems while limiting transitional difficulties.

Make the specification reasonably stable.

Gain the approval of distributors, developers, and other decision-makers
in relevant development groups and encourage their participation.

Provide a standard that is attractive to the implementors of different
UNIX-like systems.

7.4. Scope

This document specifies a standard filesystem hierarchy for FHS
filesystems by specifying the location of files and directories, and
the contents of some system files.

This standard has been designed to be used by system
integrators, package developers, and system administrators in the
construction and maintenance of FHS compliant filesystems. It is
primarily intended to be a reference and is not a tutorial on how to
manage a conforming filesystem hierarchy.

The FHS grew out of earlier work on FSSTND, a filesystem
organization standard for the Linux operating system. It builds on
FSSTND to address interoperability issues not just in the Linux
community but in a wider arena including 4.4BSD-based operating
systems. It incorporates lessons learned in the BSD world and
elsewhere about multi-architecture support and the demands of
heterogeneous networking.

Although this standard is more comprehensive than previous
attempts at filesystem hierarchy standardization, periodic updates may
become necessary as requirements change in relation to emerging
technology. It is also possible that better solutions to the problems
addressed here will be discovered so that our solutions will no longer
be the best possible solutions. Supplementary drafts may be released
in addition to periodic updates to this document. However, a specific
goal is backwards compatibility from one release of this document to
the next.

Comments related to this standard are welcome. Any comments or
suggestions for changes may be directed to the
FHS mailing list, or filed as bugs, or both.
Typographical or grammatical comments should be filed as bugs.
The bugtracker is at
http://bugs.linuxfoundation.org
- use the category FHS.

Before sending mail to the mailing list it is requested that you
first glance at the mailing list archives to avoid excessive re-discussion
of old topics.

Questions about how to interpret items in this document may
occasionally arise. If you have need for a clarification, please
contact the FHS editor. Since this standard represents a consensus of
many participants, it is important to make certain that any
interpretation also represents their collective opinion. For this
reason it may not be possible to provide an immediate response unless
the inquiry has been the subject of previous discussion.

7.5. Acknowledgments

The developers of the FHS wish to thank the developers, system
administrators, and users whose input was essential to this standard.
We wish to thank each of the contributors who helped to write,
compile, and compose this standard.

The FHS Group also wishes to thank those Linux developers who
supported the FSSTND, the predecessor to this standard. If they
hadn't demonstrated that the FSSTND was beneficial, the FHS could
never have evolved.